U.S. patent number 9,120,944 [Application Number 14/346,534] was granted by the patent office on 2015-09-01 for copper particulate dispersion, conductive film forming method and circuit board.
This patent grant is currently assigned to APPLIED NANOTECH HOLDINGS, INC., ISHIHARA CHEMICAL CO., LTD.. The grantee listed for this patent is Yuichi Kawato, Tomio Kudo, Yusuke Maeda. Invention is credited to Yuichi Kawato, Tomio Kudo, Yusuke Maeda.
United States Patent |
9,120,944 |
Kawato , et al. |
September 1, 2015 |
Copper particulate dispersion, conductive film forming method and
circuit board
Abstract
An object is to provide a copper particulate dispersion which is
suited to discharge in the form of droplets. The copper particulate
dispersion includes copper particulates, at least one kind of a
dispersion vehicle containing the copper particulates, and at least
one kind of dispersant which allows the copper particulates to
disperse in the dispersion vehicle. The copper particulates have a
center particle diameter of 1 nm or more and less than 100 nm. The
dispersion vehicle is a polar dispersion vehicle having a boiling
point within a range from 150.degree. C. to 250.degree. C. Whereby,
when the copper particulate dispersion is discharged in the form of
droplets, clogging at the discharge portion caused by drying of the
dispersion vehicle is prevented and the viscosity is low for its
high boiling point, and thus the copper particulate dispersion is
suited to discharge in the form of droplets.
Inventors: |
Kawato; Yuichi (Hyogo,
JP), Maeda; Yusuke (Hyogo, JP), Kudo;
Tomio (Hyogo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kawato; Yuichi
Maeda; Yusuke
Kudo; Tomio |
Hyogo
Hyogo
Hyogo |
N/A
N/A
N/A |
JP
JP
JP |
|
|
Assignee: |
ISHIHARA CHEMICAL CO., LTD.
(Hyogo, JP)
APPLIED NANOTECH HOLDINGS, INC. (Austin, TX)
|
Family
ID: |
47469418 |
Appl.
No.: |
14/346,534 |
Filed: |
January 4, 2012 |
PCT
Filed: |
January 04, 2012 |
PCT No.: |
PCT/JP2012/050010 |
371(c)(1),(2),(4) Date: |
March 21, 2014 |
PCT
Pub. No.: |
WO2013/073200 |
PCT
Pub. Date: |
May 23, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140216798 A1 |
Aug 7, 2014 |
|
Foreign Application Priority Data
|
|
|
|
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Nov 14, 2011 [JP] |
|
|
2011-248127 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D
11/38 (20130101); H05K 1/097 (20130101); H01B
1/026 (20130101); C09D 11/03 (20130101); C09D
11/52 (20130101); H01L 23/49883 (20130101); H05K
1/095 (20130101); H01B 1/22 (20130101); H05K
1/092 (20130101); H01L 2924/0002 (20130101); H05K
2203/0514 (20130101); H01L 2924/0002 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
C09D
11/52 (20140101); H01L 23/498 (20060101); H05K
1/09 (20060101); H01B 1/02 (20060101); H01B
1/22 (20060101); C09D 11/03 (20140101); C09D
11/38 (20140101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
2004-043776 |
|
Feb 2004 |
|
JP |
|
2004-185952 |
|
Jul 2004 |
|
JP |
|
2008-88518 |
|
Apr 2008 |
|
JP |
|
2009-105040 |
|
May 2009 |
|
JP |
|
2009-135480 |
|
Jun 2009 |
|
JP |
|
2008/051719 |
|
May 2008 |
|
WO |
|
2009/111393 |
|
Sep 2009 |
|
WO |
|
2010/114769 |
|
Oct 2010 |
|
WO |
|
2011/031118 |
|
Mar 2011 |
|
WO |
|
Other References
US. Appl. No. 14/346,519, which was filed Mar. 21, 2014. cited by
applicant .
U.S. Appl. No. 14/346,544, which was filed Mar. 21, 2014. cited by
applicant .
Extended European search report for EP Application No. 12849820.1,
mail date is Mar. 11, 2015. cited by applicant .
Korean Office Action issued for application No.10-2014-7009076,
mail date is May 18, 2015. cited by applicant .
Search Report issued with respect to International Application No.
PCT/JP2012/050010, mail date is Apr. 3, 2012. cited by applicant
.
U.S. Appl. No. 14/346,519, which was filed on Mar. 21, 2014. cited
by applicant .
U.S. Appl. No. 14/346,544, which was filed on Mar. 21, 2014. cited
by applicant.
|
Primary Examiner: Norris; Jeremy C
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Claims
The invention claimed is:
1. A copper particulate dispersion comprising copper particulates,
at least one kind of a dispersion vehicle containing the copper
particulates, and at least one kind of dispersant which allows the
copper particulates to disperse in the dispersion vehicle, wherein
the copper particulates have a center particle diameter of 1 nm or
more and less than 100 nm, concentration of the copper particulates
is 1% by weight or more and 80% by weight or less based on the
copper particulate dispersion, the dispersion vehicle is a polar
dispersion vehicle having a boiling point within a range from
150.degree. C. to 250.degree. C., the polar dispersion vehicle
contains at least one of a protic dispersion vehicle and an aprotic
polar dispersion vehicle having a dielectric constant of 30 or
more, the protic dispersion vehicle is selected from the group
consisting of diethylene glycol monobutyl ether, diethylene glycol
monomethyl ether, 2-methylpentane-2,4-diol, ethylene glycol,
propylene glycol, 1,5-pentanediol, diethylene glycol, triethylene
glycol, glycerin and sorbitol, the aprotic polar dispersion vehicle
is selected from the group consisting of hexamethylphosphoramide,
N-methyl pyrrolidone, N-ethyl pyrrolidone, nitrobenzene, N,
N-diethylformamide, N, N-dimethylacetamide, furfural,
.gamma.-butyrolactone, ethylene sulfite, sulfolane, dimethyl
sulfoxide, succinonitrile and ethylene carbonate, the dispersant is
a compound having at least one acidic functional group, which has a
molecular weight of 200 or more and 100,000 or less, or a salt
thereof, concentration of the dispersant is 0.5% by weight or more
and 50% by weight or less based on the copper particulate
dispersion, and the acidic functional group of the dispersant is
selected from the group consisting of a phosphoric acid group, a
phosphoric acid group, a sulfonic acid group and a sulfuric acid
group.
2. A conductive film forming method comprising the steps of:
discharging the copper particulate dispersion according to claim 1
on a surface of an object in the form of droplets to form a film
made of the copper particulate dispersion on the surface of the
object, drying the film thus formed, and forming a conductive film
through photo sintering of irradiating the dried film with
light.
3. A circuit board comprising a circuit including the conductive
film formed by the conductive film forming method according to
claim 2 on a substrate.
Description
TECHNICAL FIELD
The present invention relates to a copper particulate dispersion, a
conductive film forming method using the copper particulate
dispersion, and a circuit board produced by using the conductive
film forming method.
BACKGROUND ART
There has hitherto existed a printed board in which a circuit
composed of a copper foil is formed on a substrate by
photolithography. Photolithography includes the step of etching a
copper foil and high costs are required for a treatment of waste
fluid generated by etching.
There has been known, as the technology requiring no etching, a
method in which a copper particulate dispersion prepared by
dispersing copper particulates (copper nanoparticles) in a
dispersion vehicle (in a vehicle) is discharged from an ink-jet
printer on a substrate in the form of droplets to form a circuit
(see, for example, Patent Literature 1). According to this method,
a film of the copper particulate dispersion is formed on the
substrate by discharging droplets and, after drying the film,
copper particulates in the film are melted by exposure to light and
thus conductivity is imparted to the film. It is considered that
the viscosity of the copper particulate dispersion is desirably
less than 20 mPas so as to enable the dispersion to discharge in
the form of droplets. The film of the copper particulate dispersion
is dried by heating to room temperature or a temperature of
150.degree. C. or lower so that a substrate is not damaged by heat
even if the substrate is made of a resin. For the purpose of making
an attempt to reduce the amount of the dispersion vehicle which
remains after drying, a dispersion vehicle having a boiling point
of lower than 150.degree. C. is selected.
However, because of low boiling point of the dispersion vehicle,
such a copper particulate dispersion is likely to be excessively
dried to cause clogging with copper particulates at the portion
from which the dispersion is discharged in the form of droplets. In
contrast, high boiling point of the dispersion vehicle may
sometimes cause an increase in viscosity, and thus it may become
difficult to discharge the copper particulate dispersion in the
form of droplets.
CITATION LIST
Patent Literature
Patent Literature 1: U.S. Patent Application No. 2008/0286488
SUMMARY OF INVENTION
Technical Problem
The present invention is made so as to solve the above-mentioned
problems and an object thereof is to provide a copper particulate
dispersion which is suited to discharge in the form of
droplets.
Solution to Problem
The copper particulate dispersion of the present invention includes
copper particulates, at least one kind of a dispersion vehicle
containing the copper particulates, and at least one kind of
dispersant which allows the copper particulates to disperse in the
dispersion vehicle, wherein the copper particulates have a center
particle diameter of 1 nm or more and less than 100 nm, and the
dispersion vehicle is a polar dispersion vehicle having a boiling
point within a range from 150.degree. C. to 250.degree. C.
In this copper particulate dispersion, the dispersant is preferably
a compound having at least one acidic functional group, which has a
molecular weight of 200 or more and 100,000 or less, or a salt
thereof.
In this copper particulate dispersion, the polar dispersion vehicle
preferably contains at least one of a protic dispersion vehicle and
an aprotic polar dispersion vehicle having a dielectric constant of
30 or more.
In this copper particulate dispersion, the protic dispersion
vehicle is preferably a linear or branched alkyl compound or
alkenyl compound of 5 or more and 30 or less carbon atoms, which
has one hydroxyl group.
In this copper particulate dispersion, the protic dispersion
vehicle may be a linear or branched alkyl compound or alkenyl
compound of 2 or more and 30 or less carbon atoms, which has 2 or
more and 6 or less hydroxyl groups.
In this copper particulate dispersion, the protic dispersion
vehicle may have 1 or more and 10 or less ether bonds.
In this copper particulate dispersion, the protic dispersion
vehicle may have 1 or more and 5 or less carbonyl groups.
In this copper particulate dispersion, the aprotic polar dispersion
vehicle is preferably selected from the group consisting of
N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl pyrrolidone,
.gamma.-butyrolactone, 1,3-dimethyl-2-imidazolidinone and propylene
carbonate.
In this copper particulate dispersion, the acidic functional group
of the dispersant is preferably selected from the group consisting
of a phosphoric acid group, a phosphonic acid group, a sulfonic
acid group, a sulfuric acid group and a carboxyl group.
The conductive film forming method of the present invention
includes the steps of discharging the copper particulate dispersion
on a surface of an object in the form of droplets to form a film
made of the copper particulate dispersion on the surface of the
object, drying the film thus formed, and forming a conductive film
through photo sintering of irradiating the dried film with
light.
The circuit board of the present invention includes a circuit
including the conductive film formed by the conductive film forming
method on a substrate.
Advantageous Effects of Invention
According to the copper particulate dispersion of the present
invention, since copper particulates have a small particle size and
contain a dispersant, a surface of the copper particulates is
coated with the dispersion vehicle molecules and the coated copper
particulates are dispersed in a dispersion vehicle. Since a boiling
point of the dispersion vehicle was adjusted to 150.degree. C. or
higher, in case of discharging the copper particulate dispersion in
the form of droplets, it is possible to prevent clogging of the
discharge portion caused by drying of the dispersion vehicle. Since
a boiling point of the dispersion vehicle was adjusted to
250.degree. C. or lower, it is possible to easily dry a film formed
by discharging the copper particulate dispersion. Since polar
dispersion vehicle was used as the dispersion vehicle, the
viscosity is low for its high boiling point, and thus the copper
particulate dispersion is suited to discharge in the form of
droplets.
DESCRIPTION OF EMBODIMENTS
The copper particulate dispersion according to the embodiment of
the present invention will be described. The copper particulate
dispersion includes copper particulates, at least one kind of a
dispersion vehicle containing the copper particulates, and at least
one kind of a dispersant. The dispersant allows the copper
particulates to disperse in a dispersion vehicle. In the present
embodiment, the copper particulates are particles of copper, which
have a center particle diameter of 1 nm or more and less than 100
nm. A polar dispersion vehicle having a boiling point within a
range from 150.degree. C. to 250.degree. C. is used as the
dispersion vehicle. The polar dispersion vehicle is protic, or when
it is aprotic, a dielectric constant is 30 or more. The dispersant
is a compound having a molecular weight of 200 or more and 100,000
or less, or a salt thereof, and it has at least one acidic
functional group.
The copper particulates are particles of copper, which have a
center particle diameter of 1 nm or more and less than 100 nm, and
copper particulates having the same center particle diameter may be
used alone, or copper particulates having two or more kinds of
center particle diameters may be used in combination. When the
center particle diameter is 100 nm or more, the weight of particles
increases, resulting in poor dispersion stability.
The concentration of copper particulates is 1% by weight or more
and 80% by weight or less based on the copper particulate
dispersion. When the concentration of copper particulates is less
than 1% by weight, it is impossible to obtain copper particulates
in the amount enough to form a conductive film. In contrast, when
the concentration is more than 80% by weight, dispersion stability
is poor due to too large amount of copper particulates.
This protic dispersion vehicle is a linear or branched alkyl
compound or alkenyl compound of 5 or more and 30 or less carbon
atoms, which has one hydroxyl group. This protic dispersion vehicle
may have 1 or more and 10 or less ether bonds, and may have 1 or
more and 5 or less carbonyl groups. In case of having 4 or less
carbon atoms, polarity of the dispersion vehicle increases and thus
the dispersion effect of copper particulates is obtained. However,
elution (corrosion) of copper particulates into the dispersion
vehicle occurs, resulting in poor dispersion stability. In case of
having more than 30 carbon atoms, polarity of the dispersion
vehicle decreases and thus it becomes impossible to dissolve a
dispersant.
Examples of such a protic dispersion vehicle include, but are not
limited to, 3-methoxy-3-methyl butanol, triethylene glycol
monomethyl ether, diethylene glycol monobutyl ether, diethylene
glycol monomethyl ether, propylene glycol monobutyl ether, ethylene
glycol monohexyl ether, ethylene glycol mono-tert-butyl ether,
2-octanol and the like.
The protic dispersion vehicle may be a linear or branched alkyl
compound or alkenyl compound of 2 or more and 30 or less carbon
atoms, which has 2 or more and 6 or less hydroxyl groups. This
protic dispersion vehicle may have 1 or more and 10 or less ether
bonds, and may have 1 or more and 5 or less carbonyl groups.
Examples of such a protic dispersion vehicle include, but are not
limited to, 2-methylpentane-2,4-diol, ethylene glycol, propylene
glycol, 1,5-pentanediol, diethylene glycol, triethylene glycol,
glycerin, sorbitol and the like.
Examples of the aprotic polar dispersion vehicle having a
dielectric constant of 30 or more include, but are not limited to,
propylene carbonate, 1,3-dimethyl-2-imidaolidinone,
hexamethylphosphoramide, N-methyl pyrrolidone, N-ethyl pyrrolidone,
nitrobenzene, N,N-diethylformamide, N,N-dimethylacetamide,
furfural, .gamma.-butyrolactone, ethylene sulfite, sulfolane,
dimethyl sulfoxide, succinonitrile, ethylene carbonate and the
like.
These polar dispersion vehicle may be used alone, or two or more
kinds of them may be appropriately used in combination.
This dispersant is a compound having at least one or more acidic
functional group, which has a molecular weight of 200 or more and
100,000 or less, or a salt thereof. The acidic functional group of
the dispersant is a functional group having acidity, namely, proton
donor ability and includes, for example, a phosphoric acid group, a
phosphonic acid group, a sulfonic acid group, a sulfuric acid group
and a carboxyl group.
In case of using these dispersants, they may be used alone, or two
or more kinds of them may be appropriately used in combination. The
concentration of the dispersant is 0.5% by weight or more and 50%
by weight or less based on the copper particulate dispersion. When
the concentration of the dispersant is less than 0.5% by weight,
sufficient dispersion effect cannot be obtained. In contrast, when
the concentration is more than 50% by weight, in case of using the
copper particulate dispersion in a printing method, it exerts an
adverse influence on printing characteristics.
It is possible to appropriately add a viscosity modifier, a
leveling agent, a surface modifier, a defoamer, a corrosion
prevention agent, a resin component, a photo sintering modifier and
the like to these copper particulate dispersions according to
intended uses as long as dispersion stability is not impaired.
According to the copper particulate dispersion mixed as mentioned
above, since copper particulates have a small particle size and
contain a dispersant, a surface of the copper particulates is
coated with the dispersion vehicle molecules and the coated copper
particulates are dispersed in a dispersion vehicle. Since a boiling
point of the dispersion vehicle was adjusted to 150.degree. C. or
higher, in case of discharging the copper particulate dispersion
from an ink-jet printer or the like in the form of droplets, it is
possible to prevent clogging of the discharge portion caused by
drying of the dispersion vehicle. Since a boiling point of the
dispersion vehicle was adjusted to 250.degree. C. or lower, it is
possible to easily dry a film formed by discharging the copper
particulate dispersion. Since polar dispersion vehicle was used as
the dispersion vehicle, the viscosity is low for its high boiling
point, and thus the copper particulate dispersion is suited to
discharge in the form of droplets.
Since a dispersant has an acidic functional group and a dispersion
vehicle is a polar dispersion vehicle, the dispersant has
compatibility with the dispersion vehicle. Therefore, the copper
particulates having a surface coated with dispersant molecules are
dispersed in a dispersion vehicle.
When the dispersion vehicle is a protic dispersion vehicle, a
boiling point is increased by a hydrogen bond between dispersion
vehicle molecules and the viscosity is low for its high boiling
point, and thus the copper particulate dispersion is suited to
discharge in the form of droplets.
Since polarity increases when the protic dispersion vehicle has an
ether bond or a carbonyl group, the boiling point increases and the
viscosity is low for its high boiling point, and thus the copper
particulate dispersion is suited to discharge in the form of
droplets.
Since the dielectric constant is high when the dispersion vehicle
is an aprotic polar dispersion vehicle having a dielectric constant
of 30 or more, the boiling point is increased by an electrostatic
interaction and the viscosity is low for its high boiling point,
and thus the copper particulate dispersion is suited to discharge
in the form of droplets.
The inventors of the present invention have found the formulation
of the copper particulate dispersion by carrying out numerous
experiments.
The conductive film forming method using a copper particulate
dispersion of the present embodiment will be described. First, a
copper particulate dispersion is discharged on a surface of an
object in the form of droplets to form a film made of the copper
particulate dispersion on the surface of the object. The object is,
for example, a substrate made of polyimide or glass. The copper
particulate dispersion is discharged in the form of droplets by,
for example, an ink-jet printer. The copper particulate dispersion
is used as an ink for ink-jet printer, and a predetermined pattern
is printed on the object by an ink-jet printer to form a film with
the pattern.
Next, the film made of the copper particulate dispersion is dried.
The dispersion vehicle and the dispersant in the copper particulate
dispersion are vaporized by drying the film, and thus copper
particulates remain. The drying time of the film varies depending
on the dispersion vehicle, and drying is completed within 30
minutes under an air atmosphere at 100.degree. C. In order to
shorten the drying time of the film, the film may be subjected to
air flow.
Next, the dried film is irradiated with light. Copper particulates
are fired by irradiation with light. In firing (photo sintering) by
irradiation with light, reduction of a surface oxide film of copper
particulates and sintering of copper particulates occur. The copper
particulates are mutually melted in sintering and welded to the
substrate. Photo sintering is performed at room temperature under
atmospheric air. A light source used in photo sintering is, for
example, a xenon lamp. A laser equipment may be used as a light
source. Magnitude of energy of light irradiated from the light
source is within a range of 0.1 J/cm.sup.2 or more and 100
J/cm.sup.2 or less. The irradiation time is 0.1 ms or more and 100
ms or less. Irradiation may be performed once or plural times
(multistage irradiation). Conductivity is imparted to the film
subjected to photo sintering. Whereby, a conductive film is formed.
The thus formed conductive film is in the form of a continuous
film. Resistivity of the conductive film is from 2 .mu..OMEGA.cm to
9 .mu..OMEGA.cm.
The circuit board produced by using this conductive film forming
method will be described. This circuit board includes a circuit on
a substrate. The substrate is obtained by forming an insulating
material such as polyimide or glass into a plate and is, for
example, a flexible substrate or a rigid substrate. The substrate
may be composed of a semiconductor such as a silicone wafer. The
circuit includes a conductive film formed by this conductive film
forming method. The conductive film constitutes, for example, a
conducting wire which electrically connects between circuit
elements. The conductive film may constitute the circuit element or
a part thereof, for example, a coil, an electrode of a capacitor
and the like.
A copper particulate dispersion as Example of the present
invention, and a copper particulate dispersion for comparison were
prepared. The copper particulate dispersion was prepared by the
following method, and then evaluated. After weighing a
predetermined concentration, copper particulates were gradually
added to a dispersant and dispersion vehicle compatibilized
mutually, followed by mixing and stabilization at a given
temperature for a given time using a disperser. Dispersibility of
the thus prepared copper particulate dispersion was confirmed by
the fact that no precipitate is formed, and coarse particles are
absent on a film after printing. Dispersion stability was confirmed
by the fact that no precipitate is formed after storage of the
copper particulate dispersion at 5.degree. C. for one month.
Viscosity of the copper particulate dispersion was measured at
20.degree. C. using a viscometer.
The conductive film formed from the copper particulate dispersion
was evaluated by the following method. The copper particulate
dispersion was printed on a polyimide substrate in a film thickness
of about 0.5 .mu.m by an industrial ink-jet printer, dried under an
atmospheric air atmosphere at 100.degree. C. for 30 minutes, and
then subjected to photo sintering by a flash irradiation device
using a xenon lamp. Photo sintering was carried out at magnitude of
energy within a range from 0.5 to 30 J/cm.sup.2 for 0.1 ms to 10 ms
until a conductive film having optimum resistivity was obtained by
irradiation with light once or plural times.
EXAMPLE 1
Using copper particulates having a center particle diameter of 20
nm, 3-methoxy-3-methyl butanol (with proticity, boiling point:
174.degree. C.) as a dispersion vehicle, and a compound having a
phosphoric acid group which has a molecular weight of about 1,500
(manufactured by BYK-Chemie under the trade name of "DISPERBYK
(registered trademark)-111") as a dispersant, a copper particulate
dispersion was prepared. The concentration of the dispersant was
adjusted to 1.8% by weight and the concentration of copper
particulates was adjusted to 22.5% by weight. The concentration of
the dispersion vehicle is balance thereof. This copper particulate
dispersion had a viscosity of 18 mPas, which is less than 20 mPas,
desired for an ink for ink-jet printer. A conductive film formed by
photo sintering using this copper particulate dispersion had a
resistivity of 9 .mu..OMEGA.cm, and a desired value was obtained.
This copper particulate dispersion was stored at 5.degree. C. for
one month. As a result, no change occurred and thus it was
confirmed to have high dispersion stability.
EXAMPLE 2
In the same manner as in Example 1, except that the center particle
diameter of copper particulates was changed to 40 nm, a copper
particulate dispersion was prepared. This copper particulate
dispersion had a viscosity of 17 mPas. A conductive film formed by
photo sintering using this copper particulate dispersion had a
resistivity of 9 .mu..OMEGA.cm, and a desired value was obtained.
This copper particulate dispersion was stored at 5.degree. C. for
one month. As a result, no change occurred and thus it was
confirmed to have high dispersion stability.
EXAMPLE 3
In the same manner as in Example 2, except that the center particle
diameter of copper particulates was changed to 70 nm, a copper
particulate dispersion was prepared. This copper particulate
dispersion had a viscosity of 16 mPas. A conductive film formed by
photo sintering using this copper particulate dispersion had a
resistivity of 8 .mu..OMEGA.cm, and a desired value was obtained.
This copper particulate dispersion was stored at 5.degree. C. for
one month. As a result, no change occurred and thus it was
confirmed to have high dispersion stability.
EXAMPLE 4
In the same manner as in Example 3, except that the concentration
of the dispersant was changed to 1.8% by weight and the
concentration of copper particulates was changed to 10% by weight,
a copper particulate dispersion was prepared. This copper
particulate dispersion had a viscosity of 8 mPas. A conductive film
formed by photo sintering using this copper particulate dispersion
had a resistivity of 9 .mu..OMEGA.cm. This copper particulate
dispersion was stored at 5.degree. C. for one month. As a result,
no change occurred.
EXAMPLE 5
In the same manner as in Example 4, except that the dispersion
vehicle was changed to diethylene glycol monobutyl ether (with
proticity, boiling point: 230.degree. C.) and the concentration of
copper particulates was changed to 45% by weight, a copper
particulate dispersion was prepared. This copper particulate
dispersion had a viscosity of 8 mPas. A conductive film formed by
photo sintering using this copper particulate dispersion had a
resistivity of 8 .mu..OMEGA.cm. This copper particulate dispersion
was stored at 5.degree. C. for one month. As a result, no change
occurred.
EXAMPLE 6
In the same manner as in Example 5, except that the dispersant was
changed to a compound having a phosphoric acid group, which has a
molecular weight of several tens of thousands (manufactured by
BYK-Chemie under the trade name of "DISPERBYK (registered
trademark)-2001"), a copper particulate dispersion was prepared.
This copper particulate dispersion had a viscosity of 11 mPas. A
conductive film formed by photo sintering using this copper
particulate dispersion had a resistivity of 5 .mu..OMEGA.cm. This
copper particulate dispersion was stored at 5.degree. C. for one
month. As a result, no change occurred.
EXAMPLE 7
In the same manner as in Example 5, except that the dispersion
vehicle was changed to diethylene glycol monomethyl ether (with
proticity, boiling point: 194.degree. C.), a copper particulate
dispersion was prepared. This copper particulate dispersion had a
viscosity of 6 mPas. A conductive film formed by photo sintering
using this copper particulate dispersion had a resistivity of 7
.mu..OMEGA.cm. This copper particulate dispersion was stored at
5.degree. C. for one month. As a result, no change occurred.
EXAMPLE 8
In the same manner as in Example 7, except that the dispersion
vehicle was changed to a mixture of 3-methoxy-3-methyl butanol
(with proticity, boiling point: 174.degree. C.) with triethylene
glycol monomethyl ether (protic polarity, boiling point:
249.degree. C.) at a mixing ratio of 1:1, a copper particulate
dispersion was prepared. This copper particulate dispersion had a
viscosity of 15 mPas. A conductive film formed by photo sintering
using this copper particulate dispersion had a resistivity of 5
.mu..OMEGA.cm. This copper particulate dispersion was stored at
5.degree. C. for one month. As a result, no change occurred.
EXAMPLE 9
In the same manner as in Example 8, except that the dispersion
vehicle was changed to a mixture of diethylene glycol monomethyl
ether (with proticity, boiling point: 194.degree. C.) with
triethylene glycol monomethyl ether (with proticity, boiling point:
249.degree. C.) at a mixing ratio of 1:1, a copper particulate
dispersion was prepared. This copper particulate dispersion had a
viscosity of 7 mPas. A conductive film formed by photo sintering
using this copper particulate dispersion had a resistivity of 7
.mu..OMEGA.cm. This copper particulate dispersion was stored at
5.degree. C. for one month. As a result, no change occurred.
EXAMPLE 10
In the same manner as in Example 9, except that the dispersion
vehicle was changed to N,N-dimethylacetamide (with aprotic
polarity, dielectric constant: 38, boiling point: 165.degree. C.),
a copper particulate dispersion was prepared. This copper
particulate dispersion had a viscosity of 4 mPas. A conductive film
formed by photo sintering using this copper particulate dispersion
had a resistivity of 7 .mu..OMEGA.cm. This copper particulate
dispersion was stored at 5.degree. C. for one month. As a result,
no change occurred.
EXAMPLE 11
In the same manner as in Example 10, except that the dispersion
vehicle was changed to N,N-dimethylformamide (with aprotic
polarity, dielectric constant: 37, boiling point: 153.degree. C.),
a copper particulate dispersion was prepared. This copper
particulate dispersion had a viscosity of 3 mPas. A conductive film
formed by photo sintering using this copper particulate dispersion
had a resistivity of 4 .mu..OMEGA.cm. This copper particulate
dispersion was stored at 5.degree. C. for one month. As a result,
no change occurred.
EXAMPLE 12
In the same manner as in Example 11, except that the dispersion
vehicle was changed to N-methyl pyrrolidone (with aprotic polarity,
dielectric constant: 32, boiling point: 204.degree. C.), a copper
particulate dispersion was prepared. This copper particulate
dispersion had a viscosity of 5 mPas. A conductive film formed by
photo sintering using this copper particulate dispersion had a
resistivity of 5 .mu..OMEGA.cm. This copper particulate dispersion
was stored at 5.degree. C. for one month. As a result, no change
occurred.
EXAMPLE 13
In the same manner as in Example 11, except that the dispersion
vehicle was changed to .gamma.-butyrolactone (with aprotic
polarity, dielectric constant: 39, boiling point: 204.degree. C.),
a copper particulate dispersion was prepared. This copper
particulate dispersion had a viscosity of 9 mPas. A conductive film
formed by photo sintering using this copper particulate dispersion
had a resistivity of 6 .mu..OMEGA.cm. This copper particulate
dispersion was stored at 5.degree. C. for one month. As a result,
no change occurred.
EXAMPLE 14
In the same manner as in Example 6, except that the dispersion
vehicle was changed to .gamma.-butyrolactone (with aprotic
polarity, dielectric constant: 39, boiling point: 204.degree. C.)
and the concentration of the dispersant was changed to 3.6% by
weight, a copper particulate dispersion was prepared. This copper
particulate dispersion had a viscosity of 6 mPas. A conductive film
formed by photo sintering using this copper particulate dispersion
had a resistivity of 7 .mu..OMEGA.cm. This copper particulate
dispersion was stored at 5.degree. C. for one month. As a result,
no change occurred.
EXAMPLE 15
In the same manner as in Example 13, except that the dispersion
vehicle was changed to 1,3-dimethyl-2-imidazolidinone (with aprotic
polarity, dielectric constant: 38, boiling point: 225.degree. C.),
a copper particulate dispersion was prepared. This copper
particulate dispersion had a viscosity of 8 mPas. A conductive film
formed by photo sintering using this copper particulate dispersion
had a resistivity of 5 .mu..OMEGA.cm. This copper particulate
dispersion was stored at 5.degree. C. for one month. As a result,
no change occurred.
EXAMPLE 16
In the same manner as in Example 15, except that the dispersant was
changed to a mixture of "DISPERBYK (registered trademark)-111" with
"DISPERBYK (registered trademark)-2001" at a mixing ratio of 1:2
and the concentration thereof was changed to 3.6% by weight, a
copper particulate dispersion was prepared. This copper particulate
dispersion had a viscosity of 5 mPas. A conductive film formed by
photo sintering using this copper particulate dispersion had a
resistivity of 5 .mu..OMEGA.cm. This copper particulate dispersion
was stored at 5.degree. C. for one month. As a result, no change
occurred.
EXAMPLE 17
In the same manner as in Example 15, except that the dispersant was
changed to a phosphate having a phosphoric acid group, which has a
molecular weight of 1,000 or more and less than 10,000
(manufactured by BYK-Chemie under the trade name of "DISPERBYK
(registered trademark)-145"), a copper particulate dispersion was
prepared. This copper particulate dispersion had a viscosity of 10
mPas. A conductive film formed by photo sintering using this copper
particulate dispersion had a resistivity of 4 .mu..OMEGA.cm. This
copper particulate dispersion was stored at 5.degree. C. for one
month. As a result, no change occurred.
EXAMPLE 18
In the same manner as in Example 17, except that the dispersant was
changed to a low molecular polyaminoamide and an acid polymer salt
(manufactured by BYK-Chemie under the trade name of "ANTI-TERRA
(registered trademark)-U100"), a copper particulate dispersion was
prepared. This copper particulate dispersion had a viscosity of 14
mPas. A conductive film formed by photo sintering using this copper
particulate dispersion had a resistivity of 2 .mu..OMEGA.cm. This
copper particulate dispersion was stored at 5.degree. C. for one
month. As a result, no change occurred.
EXAMPLE 19
In the same manner as in Example 14, except that the dispersion
vehicle was changed to propylene carbonate (with aprotic polarity,
dielectric constant: 64, boiling point: 240.degree. C.) and the
concentration of the dispersant was changed to 1.8% by weight, a
copper particulate dispersion was prepared. This copper particulate
dispersion had a viscosity of 10 mPas. A conductive film formed by
photo sintering using this copper particulate dispersion had a
resistivity of 7 .mu..OMEGA.cm. This copper particulate dispersion
was stored at 5.degree. C. for one month. As a result, no change
occurred.
EXAMPLE 20
In the same manner as in Example 18, except that the dispersant was
changed to an alkylammonium salt of a compound having a phosphoric
acid group, which has a molecular weight of 1,000 or more and 2,000
or less (manufactured by BYK-Chemie under the trade name of
"DISPERBYK (registered trademark)-180"), a copper particulate
dispersion was prepared. This copper particulate dispersion had a
viscosity of 9 mPas. A conductive film formed by photo sintering
using this copper particulate dispersion had a resistivity of 4
.mu..OMEGA.cm. This copper particulate dispersion was stored at
5.degree. C. for one month. As a result, no change occurred.
COMPARATIVE EXAMPLE 1
In the same manner as in Example 15, except that the dispersion
vehicle was changed to propylene glycol methyl ether acetate (with
nonpolarity), a copper particulate dispersion was prepared. This
copper particulate dispersion had a viscosity of 5 mPas. This
copper particulate dispersion was stored at 5.degree. C. for one
month. As a result, a precipitate was formed and thus it was found
to have non-high dispersion stability.
COMPARATIVE EXAMPLE 2
In the same manner as in Comparative Example 1, except that the
dispersion vehicle was changed to a mixture of butoxyethyl acetate
and propylene glycol methyl ether acetate at a mixing ratio of 5:1
(with nonpolarity), a copper particulate dispersion was prepared.
This copper particulate dispersion had a viscosity of 5 mPas. This
copper particulate dispersion was stored at 5.degree. C. for one
month. As a result, a precipitate was formed.
COMPARATIVE EXAMPLE 3
In the same manner as in Comparative Example 2, except that the
dispersion vehicle was changed to diethylene glycol methyl ethyl
ether (with nonpolarity), a copper particulate dispersion was
prepared. This copper particulate dispersion had a viscosity of 2
mPas. This copper particulate dispersion was stored at 5.degree. C.
for one month. As a result, a precipitate was formed.
COMPARATIVE EXAMPLE 4
In the same manner as in Comparative Example 3, except that the
dispersion vehicle was changed to tetraethylene glycol dimethyl
ether (with nonpolarity), an attempt was made to prepare a copper
particulate dispersion. However, copper particulates were not
dispersed.
COMPARATIVE EXAMPLE 5
In the same manner as in Comparative Example 3, except that the
dispersion vehicle was changed to ethylene glycol monophenyl ether
(with proticity, which is not within a technical scope of the
present invention because of containing a phenyl group), an attempt
was made to prepare a copper particulate dispersion. However,
copper particulates were not dispersed.
COMPARATIVE EXAMPLE 6
in the same manner as in comparative example 3, except That the
dispersion vehicle was changed to diethylene glycol Butyl methyl
ether (with nonpolarity), a copper particulate Dispersion was
prepared. This copper particulate dispersion Was stored at
5.degree. c. For one month. As a result, a precipitate Was
formed.
COMPARATIVE EXAMPLE 7
in the same manner as in comparative example 6, except That the
dispersion vehicle was changed to triethylene glycol Butyl methyl
ether (with nonpolarity), a copper particulate Dispersion was
prepared. This copper particulate dispersion Was stored at
5.degree. c. For one month. As a result, a precipitate Was
formed.
COMPARATIVE EXAMPLE 8
in the same manner as in comparative example 7, except That the
dispersion vehicle was changed to diethylene glycol Dibutyl ether
(with nonpolarity), an attempt was made to Prepare a copper
particulate dispersion. However, copper Particulates were not
dispersed.
COMPARATIVE EXAMPLE 9
In the same manner as in Comparative Example 7, except that the
dispersion vehicle was changed to diethylene glycol diethyl ether
(with nonpolarity), a copper particulate dispersion was prepared.
This copper particulate dispersion had a viscosity of 4 mPas. This
copper particulate dispersion was stored at 5.degree. C. for one
month. As a result, a precipitate was formed.
COMPARATIVE EXAMPLE 10
In the same manner as in Comparative Example 9, except that the
dispersion vehicle was changed to ethanol (with proticity, 4 or
less carbon atoms, boiling point: 78.degree. C.), a copper
particulate dispersion was prepared. This copper particulate
dispersion was stored at 5.degree. C. for one month. As a result,
elution (corrosion) of copper particulates into a dispersion
vehicle occurred, and thus discoloration of the liquid occurred and
a precipitation was formed.
COMPARATIVE EXAMPLE 11
In the same manner as in Comparative Example 10, except that the
dispersion vehicle was changed to ethyl acetate (with nonpolarity),
an attempt was made to prepare a copper particulate dispersion.
However, copper particulates were not dispersed.
COMPARATIVE EXAMPLE 12
In the same manner as in Comparative Example 11, except that the
dispersion vehicle was changed to hexane (with nonpolarity), an
attempt was made to prepare a copper particulate dispersion.
However, copper particulates were not dispersed.
COMPARATIVE EXAMPLE 13
In the same manner as in Comparative Example 12, except that the
dispersion vehicle was changed to toluene (with nonpolarity), an
attempt was made to prepare a copper particulate dispersion.
However, copper particulates were not dispersed.
Comparative Example 14
In the same manner as in Comparative Example 13, except that the
dispersion vehicle was changed to 2-propanol (with proticity, 4 or
less carbon atoms, boiling point: 83.degree. C.), a copper
particulate dispersion was prepared. This copper particulate
dispersion was stored at 5.degree. C. for one month. As a result,
elution (corrosion) of copper particulates into a dispersion
vehicle occurred, and thus discoloration of the liquid occurred and
a precipitation was formed.
COMPARATIVE EXAMPLE 15
In the same manner as in Comparative Example 14, except that the
dispersion vehicle was changed to acetone (with aprotic polarity,
dielectric constant: 21, boiling point: 56.degree. C.), an attempt
was made to prepare a copper particulate dispersion. However,
copper particulates were not dispersed.
COMPARATIVE EXAMPLE 16
In the same manner as in Comparative Example 15, except that the
dispersion vehicle was changed to water (with proticity, 4 or less
carbon atoms, boiling point: 100.degree. C.) and the dispersant was
changed to an alkylammonium salt of a compound having a phosphoric
acid group, which has a molecular weight of 1,000 or more and 2,000
or less (manufactured by BYK-Chemie under the trade name of
"DISPERBYK (registered trademark)-180"), a copper particulate
dispersion was prepared. This copper particulate dispersion was
stored at 5.degree. C. for one month. As a result, elution
(corrosion) of copper particulates into a dispersion vehicle
occurred, and thus discoloration of the liquid occurred and a
precipitation was formed.
COMPARATIVE EXAMPLE 17
In the same manner as in Comparative Example 15, except that the
dispersion vehicle was changed to 1-butanol (with proticity, 4 or
less carbon atoms, boiling point: 117.degree. C.), a copper
particulate dispersion was prepared. This copper particulate
dispersion was stored at 5.degree. C. for one month. As a result,
elution (corrosion) of copper particulates into a dispersion
vehicle occurred, and thus discoloration of the liquid occurred and
a precipitation was formed.
COMPARATIVE EXAMPLE 18
Using copper particulates having a center particle diameter of 400
nm, 3-methoxy-3-methyl butanol (with proticity) as a dispersion
vehicle, and a compound having a phosphoric acid group, which has a
molecular weight of about 1,500 (manufactured by BYK-Chemie under
the trade name of "DISPERBYK (registered trademark)-111") as a
dispersant, a copper particulate dispersion was prepared. The
concentration of the dispersant was adjusted to 3.6% by weight and
the concentration of copper particulates was adjusted to 40% by
weight. The concentration of the dispersion vehicle is balance
thereof. Copper particulates were not dispersed.
As mentioned above, a copper particulate dispersion vehicle in
which the dispersion vehicle is a polar dispersion vehicle having a
boiling point within a range from 150.degree. C. to 250.degree. C.
had a viscosity, which was less than 20 mPas, suited to discharge
in the form of droplets. A conductive film formed by photo
sintering using this copper particulate dispersion had a
resistivity of 9 .mu..OMEGA.cm or less, and a desired low value was
obtained. When the dispersion vehicle is a dispersion vehicle with
nonpolarity or a dispersion vehicle having a boiling point of lower
than 150.degree. C., the obtained copper particulates were not
dispersed, or a precipitate was formed after storage at 5.degree.
C. for one month.
The present invention is not limited to the constitutions of the
above-mentioned embodiments, and various modifications can be made
without departing from the scope of the present invention.
* * * * *